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N3JIM's SWR meter

Last updated Fri, 27 May 2011

This is a low power (2 W max) SWR bridge that I built in May 2011. The electronics are pretty simple -- see the circuit description for the parts list and detailed information on the circuit.

Most of the time I spent on this project went into metalwork on the case. I've not been satisfied with my enclosures in the past, and this is an area that I've been trying to improve. This is the first project where I'm actually proud of the box! :)

Each of these small photo's link to a full-size image stored on Flickr. If you want to bypass all this text, just jump over to the QRP SWR photoset on Flickr.

Before I began working on the case, I breadboarded and tested the circuit. After I had all the external parts (UHF connectors, rotary switch, variable resistor, and 5-way binding posts), I figured out the smallest case I would need and started working on the external layout.

When I was satisfied with the layout, I started on the metalwork. Most of this was done at Sacramento City College's electronics shop/lab -- I was taking ET-306 there, and the instructor was very supportive of extra projects.

I got all the external parts mounted after the enclosure was finished, then tested the breadboarded circuit one more time. I wanted to make sure that the aluminum case was providing a suitable common "ground" for the circuit.

I soldered the discrete components together, then made all the final electrical connections. There is only one solder joint between the components and the case -- from the 3-position switch to one of the power resistors. Everything else can be unscrewed and disconnected for testing, repair, or re-work. I used #6 ring terminals for these connections, which work fine with the #4 screws on the UHF connectors and the #5 screws on the bottom of the 5-way binding posts.

This was a very satisfying project! I'm very happy with the enclosure, although in the future I think I'll use larger cases than I need.

Now that this QRP meter is done, I can start working on my copper tube Slim JIM antenna.